Various publications and patent documents are referenced in this application to describe the state of the art to which the invention pertains. Complete citations for these references are found at the end of the specification. Each of these publications or patents is incorporated by reference herein.
Sex separation of chicks at hatch is an important aspect of the poultry industry. The US poultry industry produces 8.9 billion broilers, 360 million broiler breeders, 360 million turkeys and 1.6 billion layers annually. These annual production numbers equate to roughly 160 million birds hatched each day which need to be sexed. Varied segments of the poultry industry must sex segregate offspring for different reasons. All turkeys are sex segregated due to the large differences in the growth rate, market age, management practices and nutritional requirements between male and female birds. In the layer or table egg industry, chicks must be sexed at hatch as only the females, or birds which lay eggs, are kept while all male chicks are discarded. The broiler breeder and turkey breeder industries produce both male and female lines that are eventually crossed to produce a hybrid commercial bird. The males or off-sex chicks produced from the female lines are discarded while the female chicks or off-sex chicks from the male lines are discarded. Disposal of unwanted chicks creates animal welfare and waste disposal issues for the industry. The meat type chicken or broiler industry prefer to sex segregate males from females to gain feed efficiency, improve uniformity at the processing plant and reduce production costs. The broiler industry often refrains from sex separate rearing due to the high costs of sexing and the need for trained sexers. A higher percentage of the broiler industry would sex segregate if a rapid, inexpensive, automated method were available.
Current sexing methods used in the poultry industry involve manual procedures that require highly trained professionals with specialized skills. Sexing methods involve either the Japanese method of vent sexing or feather sexing of chicks that carry a slow feathering gene (1, 2, 3). The manual sexing methods have several drawbacks. These include: 1) scheduling of manual labor; 2) increased processing time before chicks can be placed in the field with access to food and water; and 3) stress and damage to the chicks or poults. Manual sexing remains one of the few manual processing steps practiced in the highly automated poultry industry.
The Japanese or vent sexing method originated in the 1920's when the Japanese discovered that within the first or second fold of a chick's vent there are distinctive characteristics such as spots, lines and folds that reveal its sex (4, 5). Vent sexing is considered an art and generally practiced only by Asian individuals with excellent manual dexterity and Zen-like concentration (6). Vent sexers attend school for six months and then undergo a trainee program for two to five years until they are considered a qualified sexer based on speed and accuracy. Qualified sexers can vent sex 2,000 chicks per hour at 98% accuracy but only 5 to 10% of individuals attending vent sexing school attain qualified sexer status (6). The rapid rate at which a vent sexer must pick up, sex and sort baby chicks can result in a 1.4 to 1.8% increase in cull rate and 0.5 to 1.0% increase in early chick mortality due to chick damage during handling (7). Vent sexers are contract workers who travel from hatchery to hatchery working long tedious hours. Travel of these contract workers from hatchery to hatchery poses a bio-security threat for the poultry industry.
Feather sexing of chickens inbred for the K gene for slow feathering is the other commonly used method for sex segregation at hatch (3). Day-old chicks carrying the K gene can be sex segregated by examining the relative length of the primary and covert feathers of the wing, with the females carrying genes for fast feathering and the males carrying genes for slow feathering. Feather sexing is less expensive than vent sexing and does not require as skilled a labor force. Feather sexing is not applicable to turkeys, the majority of broiler breeds, some layer breeds, and also carries disadvantages. The k gene for slow feathering is closely linked to an endogenous virus (8), which can cause immunological tolerance to lymphoid leukosis (9) and is therefore a disadvantage in breeding stock. It is noteworthy that slow feathering males usually do not feather well in the brooder house especially during hot weather which often results in slower growth and increased cannibalism and that females carrying the K gene exhibit reduced egg production. Some poultry breeds exhibit sex specific color differences in feathers, however these breeds are not as commercially viable as other breeds. Color sexing can result in a higher rate of sexing mistakes than feather sexing.
Methods to sex segregate eggs before hatching have been previously attempted without success. A sex-linked gene, Sa1 for imperfect albinism was reported by Hutt and Cole (10) to have the potential to sex chicks at one day of age on the basis of eye color. The albino female chicks have pink eyes while the normal males have black eyes. The difference in eye color can also be used to accurately sex segregate embryos by candling the eggs on Day 10 of incubation. Candling or light illumination of the intact egg reveals the dark eye of the male chicken embryo but not the pink eye of the albino female. Use of the Sa1 gene to sex segregate poultry was not pursued as the gene carries deleterious effects in turkeys and negative production effects in chickens.
Development of a quick, accurate, inexpensive automated method to sex segregate eggs before hatching would significantly increase profitability of the global broiler industry. Automated sexing gives rise to several benefits. These include 1) better feed and processing efficiencies; 2) reduced incubation space requirements; 3) greater selection of breeds without constraints of selection for a slow feathering gene; 4) reduced liability and reliability concerns associated with eliminating manual labor; 5) speedier hatchery processing; and 6) reduced animal welfare concerns associated with discarding male chicks in the layer egg industry.
In light of all the foregoing, the development of a quick, inexpensive, automated method to sex segregate eggs before hatching is highly desirable.